Effect of Negative Current on the Microstructure of Oxide Coatings Prepared by Hybrid Pulse Anodization

Shuo Huang,Bailing Jiang,Qingying Shao,Cancan Liu,Hongtao Li

doi:10.3390/met9010022

Abstract

The oxide coatings were prepared on 6061 Al alloy at different negative current densities in oxalic acid using the hybrid pulse anodization (HPA) method at room temperature. The variation curves of positive and negative voltages with anodization time were recorded. The nanopore diameters and distribution regularities in HPA coatings were analyzed with the Image-Pro Plus software based on field-emission scanning electron microscope (FE-SEM) images. The results showed that the negative current could reduce the growth rate of HPA coatings, and thus led to a small thickness of the coatings within the same anodization time. Besides, appropriate negative current densities resulted in the better distribution uniformity of nanopores, but the excessive negative current densities tended to cause inferior nanopore arrangement. These were attributed to the existence of the negative current, causing H+ and O2− to move in opposite directions, so that a large number of H+ concentrated on the surface of the HPA coatings, resulting in the accelerated dissolution of the coatings.

Highlights

In the past decades, porous anodic alumina (PAA) has attracted great attention as templates to produce different kinds of functional nanostructures such as nanowires and nanotubes [1]
The low temperature was inclined to reduce the growth rate of PAA coatings, and in some cases, the processing time was even prolonged to dozens of hours [8]
6061 alloy (0.8–1.2% Mg, 0.4–0.8% Si, 0.7% Fe, 0.15–0.4% Cu, 0.04–0.35% Cr, 0.25% Zn, 0.15% Mn, 0.15% Ti, and balance Al) plates with a thickness of 3 millimeter and diameter of 35 mm were employed as substrate materials, and the area of the aluminum sample for hybrid pulse anodization (HPA) was 20 cm2

Summary

Introduction

Porous anodic alumina (PAA) has attracted great attention as templates to produce different kinds of functional nanostructures such as nanowires and nanotubes [1]. It has been in widespread use in biological sensors [2], membrane reactors [3], energy storage devices [4], and super capacitors [5] for the regular and controllable nanopores. The low temperature was inclined to reduce the growth rate of PAA coatings, and in some cases, the processing time was even prolonged to dozens of hours [8]

Methods

Results

Conclusion